Project Summary/Abstract: Funds are requested for the purchase of a dual line Nikon A1R multi-photon laser scanning microscope to support the research efforts of investigators at The Scripps Research Institute (TSRI) in La Jolla, CA. This instrument will be part of the TSRI Microscopy Core, an institutional facility available to all TSRI investigators. The requested system will replace a 12-year old Leica SP5 multi-photon laser scanning microscope. The old Leica system, which was placed in the core 2 years ago, no longer performs optimally and lacks the capabilities that are required by our user base. The 12-year old Ti:sapphire laser is unstable, has a limited tuning range, which precludes the use of commonly employed red fluors, and lacks a second line for simultaneous on-peak excitation of two fluors. The microscope stand on the old Leica system has a relatively shallow working depth, which cannot accommodate a head-holding stage or a mobile home cage. The majority of our user base require a fast multi-photon system for intra-vital imaging studies, including real-time imaging of calcium dynamics, 4-dimensional tracking of cellular movement, imaging concurrent with electrophysiological recording, imaging concurrent with behavior studies. Projects are presented by 16 investigators at TSRI, representing 9 major users and 7 minor users, of whom 15 are NIH-funded. These projects cover a broad range of biomedical studies, including neurosciences, immunology, hematology, wound healing, cancer biology, developmental biology, and cell biology. The requested system will provide much needed capabilities, currently lacking at TSRI. The system is to be configured around an open frame gantry, which will provide the flexibility to accommodate all of the users' research needs, including use of a head- holding stage, use of a mobile home cage, and access for electro-physiological recording equipment. As part of a well-used institutional microscopy core facility, the requested system will be managed according to a successful operating plan, already in place. The PI (director of the TSRI Microscopy Core) will be responsible for oversight of the system. The PI, along with the director of the Neurosciences imaging core, will be responsible for all user training and routine daily maintenance, as well as provide user assistance, consultation on experimental design, advice on system configuration and optimal system use. A Microscopy Core advisory committee is in place to govern policies concerning use of the instruments as well as resolve any disputes, should they occur. A business plan is also established, with user charges partially offsetting operating expenses. Expenses (and thus user fees) will be kept to a minimum, as the requested system will be part of the Nikon Center of Excellence at TSRI. As a Nikon CoE, TSRI receives substantial discounts on the purchase cost, as well as free instrument maintenance, free software & system upgrades, and unlimited technical support. The acquisition of a current-generation high speed multi-photon system, optimized for intravital imaging studies, is expected to have a substantial impact on NIH sponsored research at TSRI.